1. Field of the Invention
The present invention relates to a current generation supply circuit, a display device comprising the current generation supply circuit, and a drive method of the display device; and more particularly related to a current generation supply circuit applicable to driving a display panel comprised with display pixels having current control type light emitting devices and to the drive method of a driver circuit comprised with the current generation supply circuit.
2. Description of the Related Art
In recent years, as the next generation display device (display) following liquid crystal displays (LCD's), which are widely employed as monitors and displays for personal computers and video equipment, a display device which has a self-luminescent type display panel with optical devices (light emitting devices) arranged in matrix form consisting of self-luminescent type devices such as organic electroluminescent devices (hereinafter, referred to as “organic EL devices”), inorganic electroluminescent devices (hereinafter, referred to as “inorganic EL devices”) or Light Emitting Diodes (LEDs) and the like are well known.
Particularly, in comparing the liquid crystal display with a self-luminescent type display device described above, the self-luminescent type display device in which an active matrix drive method is applied provides a more rapid display response speed and there is no viewing angle dependency. Furthermore, even higher luminosity and higher contrast along with highly detailed display images using low-power consumption and the like are practicable. Also, since backlight is not needed like a liquid crystal display, this very predominant feature will lead to more thin-shaped and lightweight models. Accordingly, Research and Development (R&D) of the self-luminescent type display device which further incorporates these features into functional use is actively being pursued.
This self-luminescent type display device according to such an active matrix drive method, in general, comprises a display panel with display pixels containing light emitting devices arranged near each of the intersecting points of the scanning lines positioned in rows and the data lines positioned in columns; a data driver which generates gradation currents corresponding to the image display signals (display data) to supply each of the display pixels via the data lines; and a scanning driver which sequentially applies scanning signals at predetermined timing and sets the display pixels in specified lines to a selection state. With the above-mentioned gradation currents supplied to the display pixels, each of the light emitting devices perform a light generation operation by predetermined luminosity gradations corresponding to the display data and the desired image information is displayed on the display panel. An illustrative example of the light emitting device type display will be explained later in the embodiments of the invention.
As for the drive methods in such a self-luminescent type display device, a voltage specification type drive method which controls the current values of the drive currents flowed to each of the light emitting devices to perform the light generation operation by predetermined luminosity through adjusting the voltage values of the gradation signal voltages applied by the data driver according to the display data relative to the display pixels of specified lines selected by the scanning driver; or a current specification type drive method which controls the current values of the drive currents flowed to each of the light emitting devices through adjusting the current values of the drive currents (gradation currents) supplied by the data driver are known.
However, the self-light generation type display device mentioned above has a drawback as described below.
Specifically, of the above-mentioned methods, the voltage specification type method has to comprise pixel driver circuits which convert the voltage component of the gradation signal voltages into the current component in each of the display pixels. Therefore, when the device characteristics, such as in the Thin-Film Transistors which constitute the pixel driver circuits, are fluctuated by the external environment or deteriorate with age, the transfer characteristic from the voltage component to the current component tends to be vulnerable to the influence of these characteristic variations. Thus, variations in the current values of the drive currents become larger and result in a troublesome problem of stably acquiring the desired luminosity characteristic over a long period of time.
Conversely, the current specification type drive method has an advantage which can suppress the influence of variations in device characteristics. However, for example, when drive currents according to the display data are generated and each of the display pixels are supplied via each of the data lines based on standard (reference) currents provided via a current supply source line from a predetermined current source, since the drive currents supplied via each of the data lines changes corresponding to the display data, the standard currents supplied from the predetermined current source will also change according to the display data. Here, as a capacity component (wiring capacity) commonly exists in the signal wiring, the operation which supplies standard currents via the current supply source line mentioned above is equivalent to the charging or discharging to predetermined electric potential the capacity component which exists in the current supply source line. As a result, when the standard currents supplied via the current supply source line are extremely low, the charge and discharge operation takes time and until the electric potential of the current supply source line is stabilized, a relatively lengthy period will be required. Here, although a high-speed operation is required in the operation of the data driver, as the number of display pixels increase in proportion to the increase in the number of data lines and scanning lines, the drive period for every scanning line decreases and the time assigned to generating drive currents for every data line becomes shorter. As stated above, a certain amount of time is required for the charge and discharge operation to the current supply source line which causes a problem in the speed of the charge and discharge operation and resultant rate limitation in the operating speed of the data driver. Furthermore, when displaying image information in color, generally, the desired luminescent colors are acquired by individually controlling the light generation luminosity of the light emitting devices for each color red (R), green (G) and blue (B) according to each color component contained in the display data. As described later, since the relationship of the light generation luminosity (current-luminosity characteristic) relative to the drive currents in the light emitting devices for each RGB color differs with each other, the current values of the standard currents have to be appropriately and separately controlled according to the data lines corresponding to each color of the light emitting devices. Therefore, the drive control for producing the color display becomes complicated. In particular, it is difficult to satisfactorily control the white balance which sets the light generation luminosity of the light emitting devices of each RGB color so that the display colors can be recognized favorably as white.